1. Field of the Invention
This invention relates to electrical test apparatus for testing multiconductor cables for continuity, correct connections, and the absence of short circuits between conductors.
2. Description of the Prior Art
When multiconductor cables are connected between terminal devices, it is often necessary to perform tests to determine that the individual conductors are correctly connected to the devices, that continuity of conductors exists, and that between-conductor short circuits are not present. A relatively uncomplicated apparatus for performing such tests is disclosed in U.S. Pat. No. 3,217,244, issued to G. G. Glover on Nov. 9, 1965. The Glover apparatus comprises a first test circuit for connection to a first cable terminal device so that the cable conductors are connected by way of lamps, respectively, to a common junction point. The Glover apparatus further comprises a second test circuit for connection to a second cable termination device so that DC voltage is applied, by way of a parallel-connected resistor and lamp, between any one (hereinafter "single") conductor and the remaining conductors, collectively.
When the single conductor is continuous, correctly connected, and not shorted to another conductor, the Glover apparatus causes current to flow in a first direction in the single conductor and in the opposite direction in the remaining conductors. Because all of the current flows through the first test circuit lamp associated with the single conductor, that lamp glows. On the other hand, the current is divided between the remaining lamps so that if any glowing occurs in these lamps it is of a much less intensity. When the single conductor is discontinuous, none of the lamps glows. Furthermore, when the single conductor is misconnected, a lamp other than the expected one glows. Finally, when there is a short between the first conductor and another conductor, the lamp at the second test circuit glows.
One feature of the Glover apparatus is that the remaining conductors in a cable are connected in parallel. This is an advantage in that a good single conductor is indicated as being good notwithstanding that any one or more, but not all, of the remaining conductors is discontinuous, any number of them is misconnected, or any number of them is shorted to one another.
Another feature of the Glover apparatus is that in order to detect discontinuity and crosswiring, visual access to the lamps at the first test circuit is required. In some uses this may prove to be very time consuming. For example, when checking premises which have been prewired for multiple telephone outlets, a single craftsman using such apparatus would be required to make multiple trips between outlets.